You have a cart and a boat with a cargo hold.

We have a belt.

Originally posted by KippenKaasBaas:

We have a belt.

I think when they asked for a backpack, they meant more inventory slots.
The belt only make so you can carry more heavy stuff but it also takes up a slot in your inventory.
But I'm pretty sure there is a Backpack mod made for the game already on Nexus.

umbrella as well